A number of different applications of catadioptric imaging systems for far-field and near-field interferometric confocal and non-confocal microscopy have been described such as in commonly owned U.S. Pat. No. 6,552,852 (ZI-38) entitled “Catoptric And Catadioptric Imaging Systems” and U.S. Pat. No. 6,717,736 (ZI-43) entitled “Catoptric And Catadioptric Imaging Systems;” U.S. Provisional Patent Applications No.: 60/447,254, filed Feb. 13, 2003, entitled “Transverse Differential Interferometric Confocal Microscopy,” (ZI-40); No. 60/448,360, filed Feb. 19, 2003, entitled “Longitudinal Differential Interferometric Confocal Microscopy for Surface Profiling,” (ZI-41); No. 60/448,250, filed Feb. 19, 2003, entitled “Method and Apparatus for Dark Field Interferometric Confocal Microscopy,” (ZI-42); No. 60/442,982, filed Jan. 28, 2003, entitled “Interferometric Confocal Microscopy Incorporating Pinhole Array Beam-Splitter,” (ZI-45); No. 60/459,425, filed Apr. 1, 2003, entitled “Apparatus and Method for Joint Measurement Of Fields Of Scattered/Reflected Orthogonally Polarized Beams By An Object In Interferometry,” (ZI-50); and No. 60/485,255, filed Jul. 7, 2003, entitled “Apparatus and Method for Ellipsometric Measurements with High Spatial Resolution;” (ZI-53); and U.S. patent application Ser. No.: 10/778,371, filed Feb. 13, 2004, entitled “Transverse Differential Interferometric Confocal Microscopy,” (ZI-40); Ser. No. 10/782,057, filed Feb. 19, 2004, entitled “Longitudinal Differential Interferometric Confocal Microscopy for Surface Profiling,” (ZI-41); Ser. No. 10/782,058, filed Feb. 19, 2004, entitled “Method and Apparatus for Dark Field Interferometric Confocal Microscopy,” (ZI-42); Ser. No. 10/765,229, filed Jan. 27, 2004, entitled “Interferometric Confocal Microscopy Incorporating Pinhole Array Beam-Splitter,” (ZI-45); Ser. No. 10/816,180, filed Apr. 1, 2004, entitled “Apparatus and Method for Joint Measurement Of Fields Of Scattered/Reflected or Transmitted Orthogonally Polarized Beams By An Object In Interferometry,” (ZI-50); and Ser. No. 10/886,157, filed Jul. 7, 2004, entitled “Apparatus and Method for Ellipsometric Measurements with High Spatial Resolution,” (ZI-53). In addition, U.S. patent application (ZI-48) Ser. No. 10/218,201, entitled “Method for Constructing a Catadioptric Lens System,” filed Apr. 1, 2004 described one way to make some of these catadioptric lens systems. These patents, patent applications, and provisional patent applications are all by Henry A. Hill and the contents of each are incorporated herein in their entirety by reference.
In each of the applications of catadioptric imaging systems for each of the cited U.S. patents, U.S. patent applications, and U.S. Patent Provisional Patent Applications, tight tolerances are placed on the manufacture of optical elements. In addition to the tolerances normally encountered in designing a diffraction limited imaging system, there are tolerances imposed in interferometric confocal and non-confocal microscopy applications. The additional tolerances are for example on radii of curvature of certain imaging elements with respect to radii of curvature of certain other imaging elements and on relative locations of centers of curvature of imaging elements.
Adhering to tight tolerances can lead to improved performance of a catoptric or a catadioptric imaging system, e.g., with respect to increasing the average intensity of desired images by a factor of approximately 2 and reducing the intensity of spurious beams by one or more order of magnitudes, and in addition make it possible to realize interferometric reduction of background fields. The interferometric reduction of background fields leads to a reduction of statistical errors. The increase in intensity of desired images and the reduction of statistical errors lead to an increase in signal-to-noise ratios and to a concomitant increase in throughput of a metrology tool using the catoptric or catadioptric imaging system. The interferometric reduction of background fields further leads to a reduction of systematic errors. A consequence of the reduction of systematic errors is a reduction of the computational task required to invert arrays of interference signal values to a multi-dimensional image of an object.